No building shall be erected, rebuilt or altered, upon any land abutting on Trinity Street between Elm Street and Capitol Avenue, or upon any land abutting on Capitol Avenue between its intersection with the east line of Trinity Street and Washington Street, in the city of Hartford, to a height of more than ninety feet; but nothing herein shall prevent the erection of any tower, spire, finial, skylight, cornice or other appurtenance upon any such building to a height of more than ninety feet, provided the design or plan of such tower, spire, finial, skylight, cornice or other appurtenance shall have been approved in writing by the Commissioner of Administrative Services.